sumo69,
I currently have a MKII so the difference is huge. In any case, if there's money to be wasted, I'm there!
If you're not familiar with the differences, bimmernav.com have a good feature comparison
here.
I got it for £386 and it came from an X5.
Here's another one for sale, although it doesn't look the same as the one I bought. The eject button is different and on the right hand side whereas mine's on the left.